Gastric carcinoma is one of the most common causes of cancer-related deaths, primarily because most patients present at an advanced stage of the disease. The main cause of this cancer is the bacterium Helicobacter pylori, ...

Researchers at Michigan Medicine and in China showed that a type of bacterium is associated with the recurrence of colorectal cancer and poor outcomes. They found that Fusobacterium nucleatum in the gut can stop chemotherapy ...

Anne Woodbrey, a doctoral student, is the linchpin connecting three Dartmouth laboratories that are collaborating on a treatment for cholera—an acute diarrheal disease that can kill within hours if not treated. A recent ...

Certain fatty acids are not only part of a healthy diet—they can also neutralise the harmful listeria bacterium, a new study shows. This discovery could eventually lead to improved methods to combat dangerous and drug-resistant ...

As people across the northeastern U.S. begin venturing back into the outdoors with the arrival of spring, they will make 1 billion fewer trips than they otherwise would have if Lyme disease didn't exist, a new Yale study ...

Global Tuberculosis Report, the disease kills over 1.5 million people a year. Although the mortality rate has dropped by 47% since 1990 due to advances in preventive and treatment options, the tuberculosis bacillus is growing ...

A clever new tuberculosis vaccine has shown promise in trials in mice. If it succeeds, it will be the first new TB vaccine in a century. With the rise of multidrug resistant tuberculosis, the difficulty of curing the disease, ...

The bacteria [bækˈtɪərɪə] (help·info) (singular: bacterium)[α] are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals. Bacteria are ubiquitous in every habitat on Earth, growing in soil, acidic hot springs, radioactive waste, water, and deep in the Earth's crust, as well as in organic matter and the live bodies of plants and animals. There are typically 40 million bacterial cells in a gram of soil and a million bacterial cells in a millilitre of fresh water; in all, there are approximately five nonillion (5×1030) bacteria on Earth, forming much of the world's biomass. Bacteria are vital in recycling nutrients, with many steps in nutrient cycles depending on these organisms, such as the fixation of nitrogen from the atmosphere and putrefaction. However, most bacteria have not been characterized, and only about half of the phyla of bacteria have species that can be grown in the laboratory. The study of bacteria is known as bacteriology, a branch of microbiology.

There are approximately ten times as many bacterial cells in the human flora of bacteria as there are human cells in the body, with large numbers of bacteria on the skin and as gut flora. The vast majority of the bacteria in the body are rendered harmless by the protective effects of the immune system, and a few are beneficial. However, a few species of bacteria are pathogenic and cause infectious diseases, including cholera, syphilis, anthrax, leprosy and bubonic plague. The most common fatal bacterial diseases are respiratory infections, with tuberculosis alone killing about 2 million people a year, mostly in sub-Saharan Africa. In developed countries, antibiotics are used to treat bacterial infections and in agriculture, so antibiotic resistance is becoming common. In industry, bacteria are important in sewage treatment, the production of cheese and yoghurt through fermentation, as well as in biotechnology, and the manufacture of antibiotics and other chemicals.

Once regarded as plants constituting the class Schizomycetes, bacteria are now classified as prokaryotes. Unlike cells of animals and other eukaryotes, bacterial cells do not contain a nucleus and rarely harbour membrane-bound organelles. Although the term bacteria traditionally included all prokaryotes, the scientific classification changed after the discovery in the 1990s that prokaryotes consist of two very different groups of organisms that evolved independently from an ancient common ancestor. These evolutionary domains are called Bacteria and Archaea.